In drilling wells for the purpose of producing oil or gas from subterranean deposits, a fluid known as drilling mud is used to perform several functions necessary to successfully complete each well. This drilling fluid or mud performs many functions such as lubricating the drill string, cleaning the bore hole, and exerting sufficient pressure to the sides of the bore hole to prevent the entrance of liquids or gases into the bore hole from the formation being penetrated.
The drilling fluid must have a low fluid loss to prevent excessive loss of fluid into the formation by depositing an impervious filter cake on the sides of the bore hole. The thickness of the filter cake is usually directly proportional to the volume of fluid loss. Therefore, the lower the fluid loss the thinner the filter cake. Maintaining the diameter of the bore hole being drilled is critical to a successful operation. If the fluid loss is high, then the wall cake will be thick and therefore, the desired diameter of the well bore will be reduced.
Fluid loss additives most commonly used to control the fluid loss and also the wall cake thickness are bentonite clays, polymers, lignites, and surfactants.
Carbon black is basically pure carbon which exists in extremely small particle diameters of approximately 13 to 75 millimicrons. Carbon black particles have a high surface area. The surface area of a carbon black particle is approximately 25 to 500 square meters per gram and has an oil absorptive capacity of 45 to 300 cc per 100 grams.
Carbon black is organophilic and has an extremely high affinity for oils, phenols, alcohols, fatty acids, and other long carbon chain products normally used in drilling fluids.
Carbon black is insoluble and maintains its individual particle identity through mixing and handling procedures commonly used in the drilling mud industry. Carbon black will remain completely stable and finite at temperatures up to 3000.degree. F. The hardness of carbon black, in addition to its high affinity for lubricating substances, makes it an excellent carrier to extremely tight fittings, such as a metal to metal contact. Coated with lubricant, the ultra-fine particle size penetrates openings and scratches not normally penetrable with other solids in the drilling fluid system.
However, carbon black that has not been chemically treated is basically hydrophobic and will not readily mix with water or water based drilling fluids. Thus, it is difficult to use carbon black as an effective drilling fluid additive.